1. Field of the Invention
This invention relates to the filtering of electronic mail (hereinafter “e-mail”). More particularly, the present invention relates to a method and apparatus by which dynamic filtering techniques are applied to filter out unwanted e-mail messages at various stages of transmission across one or more networks.
2. Description of the Related Art
The rapid increase in the number of users of e-mail and the low cost of distributing electronic messages via the Internet and other electronic communications networks has made marketing via the Internet an attractive medium for productivity, workflow, advertising, and business and personal communication. Consequently, e-mail and Internet newsgroups are now frequently used as the medium for widespread marketing broadcasts. These unwanted messages are commonly referred to as “spam.”
Spam is more than just an annoyance to Internet users—it represents a significant threat to the stability of vast numbers of computers and networks which comprise the Internet community. Internet service providers (hereinafter “ISPs”), online services, and corporations spend millions of dollars each year attempting to control spam. In fact, some spam distributions are so large in scope that they have the ability to crash large ISP and corporate servers. One of the reasons why spam is so pervasive is that spammers require only a computer, an address list and Internet access to distribute spam to potentially millions of Internet users. In sum, if not properly controlled, spam is capable of disabling significant portions of the Internet.
There are a number of known methods for filtering spam including Realtime Blackhole List (“RBL”) filtering, Open Relay Blocking System (“ORBS”); and Procmail rules and recipes. Frequently, these methods are designed to block spam from particular e-mail addresses from which spam is known to originate. For example, filtering methods used by America On Line® and Prodigy® use exclusion filters which block e-mail messages received from addresses that are suspected sources of spam. However, this approach is vulnerable to rapid changes in the source of unsolicited e-mail. Furthermore, because online services will generally not automatically block e-mail addresses from their members, these services are provided only if the user requests them.
One additional known e-mail filtering techniques are based upon an inclusion list, such that e-mail received from any source other than one listed in the inclusion list is discarded as junk. However, these methods require the user or the service provider to continually update the inclusion list manually because, like viruses, spam is constantly being modified to bypass static filters. If the inclusion list is not updated regularly, the list will quickly become outdated, resulting in the exclusion of desired e-mail messages from new sources and the continued inclusion of spam from old sources.
The Assignee of the present invention has developed improved techniques for filtering e-mail. Some of these techniques are described in related U.S. patent applications entitled UNSOLICITED E-MAIL ELIMINATOR U.S. Pat. No. 5,999,992, and APPARATUS AND METHOD FOR CONTROLLING DELIVERY OF UNSOLICITED ELECTRONIC MAIL U.S. Pat. No. 6,052,709.
The present application sets forth additional techniques for filtering e-mail. What is needed is an improved system and method for dynamically updating e-mail filter technology to meet the threat posed by ever-changing varieties of spam. In addition, what is needed is a system and method for filtering e-mail which can be easily implemented by the typical e-mail user. What is also needed is an anti-spam system and method which can be applied without the need to upgrade computer systems and networks currently available.